At a basic level, wireless telecommunications systems transmit speech and data between a cellular network and a wireless telephone, hereinafter referred to as a Mobile Station (MS), over an air interface. Both the cellular network and the MS include transmitter and receiver functions, which convert information contained in the speech frequency to the frequency required for transmission through the desired medium (air and/or space). This process is called modulation.
On the MS side, the modulated speech signal is transmitted to the cellular network through an antenna on the MS. The MS antenna takes the power from the MS and radiates it out into space as radio frequency (RF) waves. The relevant range of RF waves for cellular telecommunications services are separated into different groups. The bands at 800 and 1900 MegaHertz (MHz) are reserved for cellular and Personal Communications Services (PCS) wireless systems, respectively, while the bands reserved for satellite services are scattered above 2.5 GigaHertz (GHz).
Since the frequency of an RF wave is inversely proportional to the wavelength of the RF wave, the wavelength of a satellite RF wave is substantially shorter than the wavelength of a cellular RF wave. The transmitted wavelength has a significant impact on design characteristics of the MS's, such as the size of the antenna. Typically, the smaller the wavelength, the larger the antenna needed to transmit the RF wave.
Thus, the antennas needed for satellite MS's are much larger than the antennas needed for cellular MS's. Typically, satellite MS antennas have a diameter of 15-20 mm and a length of about 14 cm. As this represents a volume of 40 to 100 percent of the leading small cellular MS's today, this alone means that the satellite MS's will be considered large in comparison to cellular MS's.
For example, one type of antenna for a satellite MS is a quadrifilar helix, which consists of four helical conducts, with a 90-degree phase shift, around a cylinder with a diameter of 15-20 mm and a length of 140 mm. Although this type of antenna provides excellent coverage for satellite transmissions, it occupies a large volume compared to the rest of the phone, which makes it difficult to design satellite MS's that are comparable in size to cellular phones. Other parameters, such as battery size, may also make the satellite MS larger, but eliminating the antenna volume on satellite MS's would yield a significant difference.
The problem is even more acute in dual-mode MS's. Dual-mode MS's have both a cellular antenna and a satellite antenna. Dual-mode MS's offer many advantages to mobile subscribers. For example, an owner of a dual-mode MS may only need to carry one MS for call origination and call delivery anywhere in the world. While in the home area, the mobile subscriber can switch the MS to cellular mode and use the cellular antenna to make and receive calls through a terrestrial cellular network, such as a Global System for Mobile Communications (GSM) network or a Digital Advanced Mobile Phone Service (D-AMPS) network. However, when the mobile subscriber roams out of the home area, instead of paying outrageous roaming charges or losing service in an unpopulated area, the mobile subscriber can switch to satellite mode and use the satellite antenna to make and receive calls through a satellite network.
However, as is the case for satellite MS's, dual-mode MS's must also include a large satellite antenna. The size of the satellite antenna alone has deterred mobile subscribers and network operators alike from investing in dual-mode MS's. In addition, the practical implications of where and how to store the satellite antenna while in cellular mode have perplexed dual-mode MS manufacturers and limited the interest in such dual-mode MS's.
It is, therefore, an object of the present invention to provide an integrated dual-mode MS having both a satellite antenna and a cellular antenna attached thereto.
It is a further object of the present invention to provide for the convenient storage of the satellite antenna within the dual-mode MS during operation of the cellular antenna.
It is still a further object of the present invention to provide for convenient activation of the satellite antenna when the dual-mode MS is in satellite mode.